One type of electrostatic pressure ink jet system is described in Sweet et al, U.S. Pat. No. 3,373,437, wherein the pressurized electrically conductive fluid is ejected from a plurality of orifices and broken into plural streams of uniform drops. As each drop breaks off from its fluid filament, it may be selectively charged by an associated charge electrode. This system operates binarily, giving a drop either a predetermined charge or leaving it in an uncharged condition. The drops then pass through an electrostatic deflection field so that the charged drops are deflected to a drop catcher or gutter, while the uncharged drops are undeflected and continue past the deflection field to impact a recording medium for printing.
The charge on a drop is established in accordance with the field produced by the charge electrode at the instant the drops break off from the filament. In the apparatus shown in U.S. Pat. No. 3,739,393 to Lyons et al, a plurality of streams is generated by forcing the ink through a set of orifices in an orifice plate and the streams are stimulated to produce drops by vibrating the orifice plate at a point near one end and propagating a traveling wave along the plate to stimulate successive orifices which causes some difference in breakoff distance in the streams and also some phase difference, that is, a difference in time between successive stream breakoffs due to the traveling wave excitation. More uniform drop breakoff is achieved in the apparatus shown in U.S. Pat. No. 3,882,508 by tapering the orifice plate along its length to compensate for the attenuation of the traveling wave along the orifice plate; however, this change does not correct the phase difference.
It is therefore the object of this invention to provide an ink jet head of simplified design which produces a plurality of ink streams each producing uniform drop breakoff and phasing.